As recently as the 1970s, wintertime flocks of evening grosbeaks used to descend on backyard feeders in Winston-Salem, North Carolina. The birds — yellow-bodied males and gray-brown females — arrived by the hundreds, devouring people’s seed supplies.
Then, gradually, they vanished.
Winston-Salem resident David Disher says the evening grosbeak has not been photographed in his home county, Forsyth, since the early 1990s.
Disher, 59, is the kind of person who would notice the absence — and what he has observed has implications for birds and their devotees all over the world.
A Human Fingerprint
An inveterate nature lover, Disher started bird-watching as a serious hobby in 1980. He has carried his binoculars to places as far-flung as South America, Australia, and, of course, Europe.
|Male evening grosbeak. (Source: Wikipedia)|
He also goes birding close to home at least once a week, and he delights in the seasonal, rotating cast of species. Time spent in nature, he says, brings a sense of freedom that you can’t find in an office building: “You can go where you want to, and do what you want to.”
So what happened to the evening grosbeak? Disher suspects climate change is responsible for their decades-old disappearance. As the climate has warmed, the species shifted its range to the north, away from Forsyth County.
In fact, bird populations all over the world show evidence of what scientists call “range shifts” — movement toward the poles or to higher mountain elevations, likely as a result of climate change.
Such shifts could severely threaten nearly half of all North American bird species, according to a report published this fall by the National Audubon Society, a conservation group. By 2080, the report says, dozens of species could be headed for extinction.
“That’s something that we should all care about, first of all, because we all love birds, and second, because birds play such a critical role in keeping ecosystems in balance,” says David Yarnold, president and CEO of Audubon.
Like many serious birders, Disher records observations in eBird, a website that allows people to submit lists of birds seen or heard during outings. Birders reported more than 3.1 million data points about North American birds in March 2012 alone, according to the site.
Scientists are using such data from amateur naturalists to track population movements, says Camille Parmesan, a biologist with appointments at the University of Texas, Austin, and at Plymouth University in the United Kingdom. “Citizen science is incredibly important to the scientific work on documentation of range shifts,” says Parmesan, widely acknowledged to be among the world’s foremost experts on the issue of bird species and climate.
Parmesan says data show a northward shift of breeding ranges for birds in the United States. Migrant birds are also arriving sooner in the calendar year — on average, two weeks early.
“These are big changes that any experienced birder is going to be noticing,” she says.
Warm Enough to Stay
|Rufous hummingbird. (Source: Wikipedia)|
One obvious change is in the habits of rufous hummingbirds. These small, vividly colored birds with slender bills used to be only visitors to the southeast United States. They would summer there, flying back to the tropics for winter.
Then, in the mid-1990s, birders participating in wildly popular annual Christmas bird counts, important data-gathering events for bird watchers, reported sightings of the bird at the peak of winter.
“Suddenly, within a few years, it wasn’t just the one or two odd sightings,” Parmesan says. “It was hundreds of individuals that were forming overwintering populations.”
That change — to become a year-round resident rather than a migrant — is “an enormous shift in status for something like a bird,” she adds.
Searching For Food and Shelter
But for many birds, adapting to climate change isn’t as simple as just picking up and moving to a new home.
Some studies suggest that birds in new habitats could have trouble finding food, such as insects and seeds, Parmesan says. The reason: Even if insects and plants move to new locations, they won’t necessarily appear in the spring at the same time when hungry migrant birds arrive. This problem of mistiming has been documented, for example, in the Netherlands, where scientists have found that the period of time when caterpillars are most abundant had fallen out of sync with the breeding dates of tits, a family of birds.
But Parmesan says it’s difficult for scientists to know for sure how the timing of food resources is changing, because they don’t have as much citizen data on insects and plants as they do on birds. There is, after all, no annual Christmas spider count.
Shelter could also pose a problem to birds. The golden-cheeked warbler of central Texas, for example, makes its nests only out of the bark of very old juniper trees. “It cannot just shift northward, because it won’t use anything else as a nest, Parmesan says. “If it doesn’t have the very old juniper trees, it will abandon the area.”
For his part, Disher worries that future generations of birders won’t be able to enjoy birds in the diversity or numbers that he has seen in his lifetime. Take the cerulean warbler, a small blue bird that migrates to the United States from the Andes Mountains. The Audubon report projects that by 2080, climate change will have pushed the species out of 98 percent of its current summer range.
Disher recalls that in the early 1980s, it was typical to see one or two cerulean warblers during spring bird counts, “Now, if one’s seen at all in the county, it is considered to be a very rare sighting,” he says.
Erika Street Hopman contributed reporting for this piece.